Communication system and communication instruments

A master communication device, comprising:

• hardware processing circuitry;
• and
• at least one memory storing instructions that, when executed by the hardware processing circuitry, cause the hardware processing circuitry to perform operations, the operations including:
• causing a slave communication device connected to the master communication device to perform a first distance measurement communication for measuring a distance between a terminal and a vehicle through a wireless communication between the terminal and the slave communication device;
• causing the master communication device to perform a second distance measurement communication for measuring a distance between the terminal and the vehicle through a wireless communication between the terminal and the master communication device;
• receiving, at the master communication device, a first result of the first distance measurement communication performed by the slave communication device and notifying, from the master communication device, a controller of the first result;
• and
• notifying, from the master communication device, the controller of a second result of the second distance measurement communication performed by the master communication device;
• wherein only the master communication device of the master communication device and the slave communication device is configured to communicate with the controller, and
• wherein actuation of the vehicle is permitted in response to any one of the first result or the second result indicating that the distance is valid.